标题: 还是问PREP数学，已解决 [打印本页] 作者: 暗绯莎 时间: 2010-4-9 22:50 标题: 还是问PREP数学，已解决 Each employee on a certain task force is either a manager or a director. What percent of the employees on the task force are directors? (1) The average (arithmetic mean) salary of the managers on the task force is $5,000 less than the average salary of all employees on the task force. (2) The average (arithmetic mean) salary of the directors on the task force is $15,000 greater than the average salary of all employees on the task force.
答案是C。。。不会做。。。作者: redo 时间: 2010-4-10 14:53
D=No. of directors, M=No. of managers, Ad=the average salaries of directors, Am=the average salaries of managers, ask for D/(D+M). Ad-Am=20000. Ad-15000=(Ad*D+Am*M)/(D+M)=Ad*D/(D+M)+Am*M/(D+M)=Ad*D/(D+M)+(Ad-20000)*(1-D/(D+M)=Ad*D/(D+M)+Ad-Ad*D/(D+M)-20000+20000*D/(D+M)=Ad-20000+20000*D/(D+M). D/(D+M)=5000/20000=1/4 考试时，碰见这种题，认倒霉吧作者: 暗绯莎 时间: 2010-4-10 15:52
恩，恩，了解了 主要是没有算到最后，想想两个方程四个未知数肯定算不出来的。。。